1. Field of the Invention
This invention relates to polyorganosiloxane sealant compositions which cure in the absence of oxygen.
2. Description of the Prior Art
Anaerobically curing sealant compositions have been known for a long time. The "oxygenated" acrylate-containing anaerobic monomers of Burnett, et al, U.S. Pat. No. 2,628,178 were subsequently improved by Krieble, U.S. Pat. No. 2,895,950. Gorman, et al., U.S. Pat. No. 3,425,988 extended the concept of anaerobic sealants from the polyalkylene either monomers of Burnett, et al. and Krieble to polymerizable monomers prepared by reacting an organic polyisocyanate with an acrylate ester containing a hydroxy or amine group in the nonacrylate portion thereof. Further improvements in anaerobically curing sealant compositions have been confined essentially to components other than the polymerizable monomer.
Polyorganosiloxane compositions are well known to possess low temperature flexibility and high temperature stability that are superior to most "organic" polymers. In spite of the fact that acrylate-containing silanes and siloxanes have been known for a long time and polymerization and copolymerization of silicon-containing acrylates have been reported, and anerobically curing polyorgnosiloxane composition has not been disclosed.
Merker, U.S. Pat. No. 2,793,223 describes the preparation of siloxanes having units of the formula ##STR1## AND THE COPOLYMERIC SILOXANES HAVING COPOLYMERIZED THEREWITH UNITS OF THE FORMULA ##STR2## WHERE N = 1 TO 2, M = 1 TO 3, R.sup.1 is H or CH.sub.3, R.sup.2 is a monovalent hydrocarbon radical and R.sup.3 is acetoxymethyl, monovalent hydrocarbon radicals or halogenated monovalent hydrocarbon radicals.
Merker, in U.S. Pat. No. 2,956,044 teaches a process for the preparation of modified acrylic resins which comprises subjecting the compositions of U.S. Pat. No. 2,793,223, where m can be zero as well as 1 to 3 inclusive, to conditions of polymerization capable of generating free radicals. Furthermore, Merker in U.S. Pat. No. 2,922,806 describes organopolysiloxanes containing polymeric units of the formula ##STR3## AND COPOLYMERS THEREWITH HAVING ADDITIONAL COPOLYMERIC UNITS OF THE FORMULA ##STR4## where n = 2 to 4, y = 0 to 1, R.sup.1 is H or CH.sub.3, R.sup.2 is a monovalent hydrocarbon radical free of aliphatic unsaturation and R.sup.3 is a monovalent hydrocarbon radical or a halogenated monovalent hydrocarbon radical. The compositions of U.S. Pat. No. 2,922,806 can be further polymerized by exposure to "vinyl polymerizing conditions."
The anaerobically curing compostions of Krieble and Gorman, et al., said to be stable if a moderate amount of air is present with the composition, for example, a small layer of air in a properly shaped and sealed glass container or a polyethylene container. It is well known that polyorganosiloxanes are permeable to oxygen and contain relatively large amounts of dissolved oxygen. It was therefore surprising to find that certain acrylate-containing polyorganosiloxane compositions can be used to formulate anaerobically curing compositions in spite of this relatively large solubility of oxygen in polyorganosiloxanes.